This sign is at the intersection of State Route 168 and Hwy 395. It is indicating that it is 24 miles east on Hwy 168 to the Ancient Bristlecone Pine Forest. This is the road you want to take as it is paved all the way there. Here is a good set of directions I found (that shows 23 miles from this junction):

From Bishop drive south on US Highway 395 for 15 miles and turn left onto State Route 168 East. Follow the road for 13 miles then turn left onto White Mountain Rd (a much smaller, but still paved road). Ten miles further you will arrive at the Schulman Grove Visitor Center. It takes a little over an hour to get to the grove on winding mountain roads.